This application's major objective is to test the efficacy of a potential microbicidal agent to prevent transmission of HIV to women. Such an effective agent is urgently needed to combat the predominant rise globally of new HIV infections in women. Based on promising preliminary results in vitro, the specific aim of this application is to test in vivo the efficacy of glycerol monolaurate (GML) to prevent intravaginal transmission of simian immunodeficiency virus (SIV) to rhesus macaques, a highly relevant nonhuman primate model of sexual mucosal transmission of HIV. Treated or control monkeys will be infected and biopsy and necropsy specimens will analyzed by immunohistochemical and in situ hybridization methods and viral loads in blood to assess the efficacy of GML in preventing transmission or altering viral replication in cervicovaginal and lymphatic tissues.